The naphtha from catalytic cracking typically contains substantial amounts of both sulfur and olefins and is a major contributor to sulfur in the gasoline pool. Due to environmentally driven regulatory pressures, the demand for lower sulfur gasoline is increasing. This implies that increasing severity in hydrotreating processes to reduce sulfur (HDS) in olefinic cracked naphthas is required. Deep HDS of these naphthas requires improved technology to avoid olefin saturation that results in high-octane loss across the process. The invention relates to a hydroprocessing catalyst, a method for preparing a hydroprocessing catalyst and a process for using same to provide reduced sulfur gasoline and gasoline additives with maintained octane levels.
The naphtha hydrodesulfurization process usually runs at high temperature, and a pressure over 400 psig, and the catalyst used typically involves non-noble metal sulfided species supported over an inorganic refractory material. The most commonly used metallic phases are CoMoS and NiMoS. A conventional hydrodesulfurization catalyst has both hydrogenation and desulfurization activities. When naphthas with high olefin content are desulfurized, it is desirable to minimize hydrogenation even with the fresh catalyst to reduce olefin saturation and the resulting octane-loss. Further, the octane loss increases with the severity of the desulfurization conditions.
Olefinic cracked naphthas (and coker naphthas as well) typically contain more than 20 wt % olefin. During a conventional hydrodesulfurization process (HDS) at least a portion of the olefins are hydrogenated, and this reaction increases for higher sulfur reduction in the feedstock. Since olefins are a high octane number species, it is desirable to retain them as much as possible. In conventional HDS processing for cracked naphtha, additional refining processes, such as isomerization, sweetening and blending, are required to produce high-octane fuels. Such additional processing adds significantly to the costs of production.
It is the primary object of the present invention to provide a suitable catalyst and a process for using same. The catalyst is selective to desulfurization of cracked naphtha with high olefin content while minimizing octane-loss with a demonstrable stability running at low hydrogen pressures.
Other objects and advantages of the present invention will appear herein below.